The VLA Observe File

The VLA observe file controls the actions of the antennas and some of the electronics. This file consists of an identifier card and an unlimited number of source request cards, including comment cards. As well, local oscillator, fine tuning, and data select cards can be added, but need not be present if the observations conform to the standards discussed in Section 7. The contents of the VLA observe file are described briefly below, with emphasis on applications to VLBI observations.

The identifier card must be the first card in the observe file and has the following column contents:

Col.  1- 2:

Identifier `` /.''.

Col.  3- 8:

VLA program code - e.g., bq001.

Col.  9-13:

VLA program number (I4). Normally 600 for VLBI.

A source request card has the following column contents:

Col.  1-13:

Source name with no imbedded blanks plus a numerical source qualifier. SCHED allows source names up to 12 alphanumeric characters in length. By default the numerical qualifier is ``0'', implying a blank so no characters are needed for it; this allows SCHED users to specify a source name of 12 or fewer alphanumeric characters (e.g., source name ``J1234$+$5659A1'', no source qualifier). If the numerical qualifier requires Q digits, then Q$+$1 characters are reserved for it because at least one blank character must separate the name and qualifier fields (e.g., source name ``J1234$+$56'', source qualifier ``1667'').

Col. 14:

A1, time code. Blank means LST stop times, ``$'' means LST durations, ``U'' means UT stop times, and ``#'' means UT durations. The final observe file must be in LST stoptimes or durations.

Col. 15-16:

I2, right-justified hours of stop time or duration depending on col. 14.

Col. 18-19:

I2, right-justified minutes of stop time or duration depending on col. 14.

Col. 21-22:

I2, right-justified seconds of stop time or duration depending on col. 14.

Col. 24-25:

I2, right-justified hours of right ascension.

Col. 27-28:

I2, right-justified minutes of right ascension.

Col. 29-36:

F8.4, seconds of right ascension.

Col. 38:

A1, sign of declination. One of plus($+$), blank, or minus($-$). Blank implies $+$.

Col. 39-40:

I2, right-justified degrees of declination.

Col. 42-43:

I2, right-justified minutes of declination.

Col. 44-50:

F7.3, seconds of declination.

Col. 51:

Epoch of position. Blank means standard equinox of 1950.0, ``D'' means apparent position of date, ``C'' means standard equinox of 2000.0, and ``Y'' means equinox of the year specified in col. 52-55.

Col. 52-55:

Equinox if ``Y'' specified in col. 51.

Col. 56-57:

VLA observing band. For a backend bandwidth of 50 MHz, the VLA band center frequency will be 1664.9 MHz for VLA band ``VL''; 4985.1 MHz for VLA band ``VC''; 8414.9 MHz for VLA band ``VX''; 15364.9 MHz for VLA band ``VU''; 22235.1 MHz for VLA band ``VK''; and 43135.1 MHz for VLA band ``VQ''. For a backend bandwidth of 25 MHz, the band center frequency will be 335.1 MHz for VLA band ``VP''. See Table 2.

Col. 59-60:

Observing mode. Blanks for normal interferometer continuum mode; ``VS'' for single-antenna VLBI; ``VA'' or ``VX'' for phased-array VLBI. Three other phased-array modes are available (``VR'' for autophasing the VLA's RCP IFs A and B; ``VL'' for autophasing the VLA's LCP IFs C and D: and ``VB'' for autophasing VLA IFs B and C); consult Joan Wrobel or Greg Taylor (see Section 17) before using these modes. ``IR'' means interferometer reference pointing mode, potentially of interest to 43-GHz observers.

Col. 61:

Calibrator code. Blank means not a calibrator. Other meanings for these codes depend on whether the calibrator was selected from the ``VLA Calibrator Manual'' or from the VLBA's Standard Source Catalog distributed with SCHED.

Col. 65-68:

Bandwidth code for backend filters. ``0000'' implies 50 MHz and should be used for all standard observations except at 0.33 GHz. At 0.33 GHz specify ``1111'' to get a bandwidth of 25 MHz. See Table 2.

Col. 69:

Reference pointing flag, potentially of interest to 43-GHz observers.

Col. 70:

System-temperature correction. This column should be left blank, to permit the real-time application of system temperature corrections. See Section 10 and Section 16.1.

Comment cards can appear anywhere in the observe file following the fileid card. Comment cards must not extend beyond column 80. They have the following column contents:

Col.  1- 4:

Identifier, which is ``//* ''.

Col.  5-80:

Alphanumeric character string.

Observe files can also contain a pair of cards, called local oscillator and fine tuning cards to tune the VLA electronics during the scan controlled by the immediately preceding source request card. The local oscillator card has the following column contents:

Col.  1- 4:

``//LO'' identifies the local oscillator card.

Col.  5- 6:

Control application of the phase switching for IF pairs AC and BD, respectively. Introduce phase switching modulation at L7 if value is zero or blank, or at F2 if value is unity and at ``L'' band. Overridden for the reference antenna if mode is ``VS''.

Col.  7-13:

F7.1, frontend LO frequency for AB IFs in GHz. Called $F_1$ or $F_{1hi}$ in Section 13.

Col. 14-20:

F7.1, frontend LO frequency for CD IFs in GHz. Called $F_1$ or $F_{1lo}$ in Section 13.

Col. 26-30:

I5, right-justified synthesizer frequency for AC IFs but rounded to the nearest MHz. Called $F_6$ in Section 13.

Col. 36-40:

I5, right-justified synthesizer frequency for BD IFs but rounded to the nearest MHz. Called $F_6$ in Section 13.

Col. 46-54:

F9.1, PT F1 frequency.

Col. 55-58:

I4, bandwidth code for frontend filters. ``0000'' implies 50 MHz; ``1111'' implies 25 MHz; and ``2222'' implies 12.5 MHz. The 25- and 12.5-MHz frontend filters are often used to reduce the effects of RFI. Standard VLBI at 0.33 GHz is done with 25-MHz frontend filters. See Table 2.

Col. 61-70:

Left-adjusted name of file containing gain calibration parameters. See Section 16.3.

Col. 71-80:

Left-adjusted name of file containing frontend and subreflector parameters. See Section 16.3.

The fine tuning card has the following column contents:

Col.  1- 4:

``//FI'' identifies the fine tuning card.

Col.  5:

Synthesizer setting code. Unless ``S'' is specified, all subsequent card parameters will be ignored!

Col. 10:

Select Fluke set 1 or 2 to use. Normally, phased-array VLBI is done with Fluke set 1 and single-antenna VLBI is done with Fluke set 2. You are encouraged to leave this entry blank, so the VLA operator is free to assign a Fluke set to the VLBI subarray.

Col. 17-30:

Fluke synthesizer A frequency in MHz. Called $F_A$ in Section 13.

Col. 37-50:

Twice the Fluke synthesizer B frequency in MHz. Called $2 \times F_B$ in Section 13.

The data select card has the following column contents:

Col.  1- 4:

``//DS'' identifies the data select card.

Col.  6- 8:

Left-justified correlator mode selection. Normally blank for VLBI implying continuum mode.

Col. 16-18:

Right-justified integration time in seconds. Phased-array VLBI is normally done with an integration time of 10 s. Single-antenna VLBI in subarray 2 is forced to use the integration time specified by the program using subarray 1.